*{
    margin:0;
    padding:0;
}

.container{
    width: 600px;
    height: 600px;
    background-color:aqua;
    border:20px solid skyblue;
    margin:20px auto;
    display: flex;
    justify-content: center;
    align-items: center;
    position: relative;
}

.container button{
    border:none;
    outline: none;
    font-size: 30px;
    color:#fff;
}

.Start-btn{
    width: 200px;
    height: 80px;
    background-color: goldenrod;
    border-radius: 20px;
    display: block;
}

.Stop-btn{
    width: 200px;
    height: 80px;
    background-color: burlywood;
    border-radius: 20px;
    display: none;
}